Natural and Synthetic Metabolic Architectures.

Metabolic engineering often treats microbial metabolism as an inventory of metabolites, reactions, and the enzymes that catalyze them. This Perspective argues that function emerges from metabolic architecture, the connectivities that bind reactions into stable regimes shaped, among other factors, by space and time. The Japanese Metabolism movement motivates an architectural view in which the same metabolites could lead to rather different phenotypes when cells reconfigure metabolic routing subjected to environmental constraints. Natural examples, including the native cyclic glycolytic wiring of Pseudomonas putida, show how redox supply and carbon flow depend on regime-level organization and space-influenced state changes. The same principles explain why microbial engineering often fails when intermediates leak, cofactors are misallocated, or timing breaks productive hand-offs. Serine-based synthetic cycles for one-carbon assimilation expose these limits as they must couple carbon entry, redox demand, and amino acid pool control around a chiral metabolite linked to translation. The emerging picture is that future designs should make routing, insulation, compartmentalization, and metabolic segregation explicit engineering targets.